The hoof problem previously known as Hoof Wall Separation Syndrome (HWSS) has been renamed as Hoof Wall Separation Disease (HWSD). HWSD is an unique, verifiable and testable disease. It should not be confused with any other hoof pathology. HWSD is a genetic autosomal recessive condition. Two carrier parents being bred with each other results in 1:4 chance of the foal being HWSD afflicted. There is now a commercially available genetic test for the HWSD mutation.

Sunday, 16 June 2013

Guest Post by Tom Ryan FWCF on his experience with treating an HWSS affected pony.

This paper has recently been published in Forge Magazine and is republished here with kind permission from Mr Ryan http://www.equinehoof.co.uk/hwss.php

Hoof wall separation syndrome in Connemara ponies

Tom Ryan FWCF

The first time I saw pony Liam (name changed)
was just after my client had bought him. I could see that he had slightly
broken up hooves but thinking like most farriers would, I expected his hooves
would improve under my charge. Unfortunately, this was not to be the case and
as the winter progressed his hooves gradually deteriorated and by April 2010
the stratum externum was breaking away from the stratum medium, not just in the
area around the nails but also around the toe of the hoof, an area that
normally stays intact when hooves break up.

Photograph 1: Liam's broken hoof in May 2010

As all four hooves were badly affected and
thinking that a bacterial infection was causing the problem I decided to ask
the help of the client's vet and together we took biopsies from the affected
areas of Liam’s hoof wall. The results came back as normal, no abnormal
bacteria associated with breaking hooves were found in the hoof.

Photograph 2: Broken hoof removed and hoof poulticed with iodine

We decided
that the entire areas of broken hoof should be removed but doing this to all
four hooves at once was out of the question as it would make the pony very
lame. Instead we decided to treat one hoof per week, in this way if we
encountered problems it would be with only one foot. So each week all the
broken hoof from one foot was removed and for the next twenty four hours the
hoof was poulticed with iodine to ensure the hoof was sterile.

Photograph 3: Kerckheart Aluminium shoe glued to repaired hoof

The hoof was rebuilt with glue then an aluminum shoe was glued to the repaired hoof, blue children's modeling
dough was used on the inner border of his shoe to prevent the glue or shoe
pressing onto the sole of his foot. This was time consuming and expensive but worked well. For the next few months the glued on shoes were replaced as they started to become loose or were lost altogether,
Liam was comfortable in the shoes and they didn’t cause him any problems.

Photograph 4: All hooves repaired

I noticed his hoof reacted slightly differently
to the glue, in that the surface of stratum medium adhered less well to the
glue, something I had not observed in other types of broken hooves. I have
experienced cases of breaking hoof walls and seedy toe in other breeds both in
everyday practice and as a referral farrier at an equine veterinary practice
and I can safely say that Liam’s feet were different, although at the time I
wasn’t sure quite how, it certainly was not a case of severe seedy toe.

When the
wall had re-grown down to the ground surface, I could still see that his hoof
was still not normal but tried again using nailed shoes, unfortunately his
hooves soon started to deteriorate again. In discussion with the client it was
decided to try Liam barefoot as an alternative solution to the problem but Liam
soon became very uncomfortable and foot sore, as all his weight was being
carried by his sole, as the hoof wall was crumbling away, we realised
that this was not going to solve his problem and went back to gluing his shoes.

Liam had
been bought for showing but as his feet were repaired with glue and the rules
for showing do not allow filled or rebuilt hooves, he could not be shown. Considering
that the only way of keeping him sound was with rebuilt hooves and glued shoes,
meant his hooves were going to be a perpetual and very costly problem. After a
lot of soul searching, the owner in discussion with her vet decided he would
have to be put down.

It was
eighteen months later at a Farriers Focus Day, that a farrier who has produced
a horseshoe for broken hooves called GluShu[ii]
first mentioned hoof wall separation syndrome in Connemara ponies to me. Some
quick research on the internet[iii]
revealed that there did seem to be an ongoing hoof wall problem within the
Connemara population which some were calling ‘Hoof Wall Separation
Syndrome‘(HWSS). Gauging what proportions of Connemara's have had problems or
how severely it has affected them was difficult to establish, certainly some
severe cases have eventually resulted in euthanasia.

Some contributors reported an apparent absence
of lipids in HWSS affected hooves, a type of fat normally found in hoof, its
function is thought to provide protection to the hoof structure by repelling
excess moisture. Reading the comments of others about HWSS, I knew that this
was what I had been dealing with eighteen months earlier.

Current thinking is that HWSS is a congenital
genetic problem, the genes thought to be responsible are said to be recessive
within an autosomal chromosome, autosomal chromosomes are not responsible for
deciding the sex of the animal and therefore both males and females can carry
the defective gene. Both parents must be carriers of the defective recessive
gene in order to produce a chance of a foal with affected hooves. The possible
outcomes are; a 1:4 chance that the foal will have HWSS, a 2:4 chance of a foal
with good hooves but still a carrier of the defective gene and a 1:4 chance of
producing a foal which is not a carrier and has good hooves.

Diagram 1: Possible outcome if both parents are HWSS carriers.

These chances are random and any outcome is possible for each foal born.

If one
parent is a HWSS carrier and the other is not, then there will be a 2:4 chance
of the foal being a carrier but it will not have HWSS hooves.

Diagram 2: Possible outcome if one parent is a carrier

The genome
for the horse was sequenced for the first time in 2007, opening the opportunity
to isolate which genes may be involved in HWSS. Currently research into HWSS is
being carried out by Dr. Carrie Finno, DVM, PhD at University of California
Davis and is focused on identifying the genes which are associated with the
production of keratin, the protein which is used to produce horn and hair. DNA
samples of both normal and affected animals are currently being collected and
compared. The goal of this research will be the ability to identify carriers of
HWSS with a simple blood test. So they can be isolated and excluded from any
future breeding program (* editor's note). Until then it will only be when an affected foal with
HWSS is born that it will alert the breeder that its parents are both carries
of HWSS. As this may not be the first foal from this dam and sire, previous
foals may have already been produced and unknowingly sold on, as there were no
indicators at that time there was a genetic problem.

When only a few ponies were carriers the
chances of both parents being affected must have been small, the odd foal with
poor quality hooves would have been seen as a random occurrence of bad luck.
Other foals would have been born as carriers with good hooves, in this
insidious way HWSS has secretly crept into the population and as the ponies
have moved around the world, so has HWSS. Today cases have been reported in
many countries including UK, Ireland, Sweden, New Zealand and the USA.

From the one case that I have experienced,
Liam's problems were of a greater magnitude than any broken hoof I had met
before. The only solution to avoid future cases of HWSS will come from revised
breeding practices which acknowledge the underlying genetic causes. If the
first-class reputation of the Connemara is to be upheld, then both breeders and
individuals will have to address this problem in an open and honest way.

First published in the Connemara Chronicle Vol
40-2013, page 183

Anatomy
notes

The hoof wall
is comprised of tubules of keratin which grow downward from the Coronary band.
Distribution or the density of the horn tubules reduces through the three main
zones of the hoof wall, the stratum externum, stratum medium and stratum
internum. The greatest density of horn tubules is in stratum externum where on
the surface of the hoof wall they are slightly flattened to become oval, which
is thought to help retain moisture. The stratum medium forms the bulk of the
hoof wall while the inner stratum internum has the lowest number of horn
tubules and forms the laminal interface with the dermal tissues, it is usually
un-pigmented and can be seen as a white line on darker coloured hooves

Diagram 3, Anatomy of hoof wall

Between the horn tubules is inter-tubular
horn which binds the horn tubules together, this has intermediate filaments
which are laterally orientated fibres which help to bind the horn tubules
together and resist cracking.

The outer stratum externum is more rigid
than the more flexible stratum medium, while the stratum internum is the
softest, this gradient of reducing stiffness helps the hoof capsule transfer
energy smoothly between the wall and the dermis and also allows the hoof
capsule to expand in shape under loading and return back to it's original shape
when the load is removed. Transfer of weight from the skeletal structures is
primarily from distal phalanx (pedal bone) via the hoof wall to the ground
surface, the solar surface can only support a small proportion of the total
weight of the horse before it causes pain.

* Editor's note. Removing carrier ponies from the breeding population is not recommended as this will further reduce an already truncated genepool; the test will identify carriers. This information will help breeders to choose non-carrier mates and therefore prevent the production of any further affected ponies.

About Me

Connemara Pony breeders from many countries have combined together to enable this research on HWSD. It is a truly international co-operative. The Research Group is completely independent of and non-aligned from any breed society or country.